The invention relates to storage and mixing of agents of which at least one is a liquid.
Many compositions which have a very short shelf life may be formed by mixing a pair of components which each has a long shelf life. The components may have the form of a powder and a liquid, respectively, and the mixing may be obtained by dissolving the powder in the liquid, but also the mixing of two liquids may lead to the provision of the wanted composition.
The wanted composition may be a solution or a suspension of a medicament in a liquid where the composition resulting from the mixing is usable for injection. E.g. solutions containing certain proteins have shown to be very sensitive and it is therefore preferred to store the dried protein isolated in a vial and to mix it with a solvent, which is similarly isolated stored, a short time before the use of the composition. It shall be noticed that a composition also may be obtained by mixing two liquids which are each stored in its own container as they react with each other in a way which results in a short shelf life for the composition.
When the composition is a medicine for injection, the containers with the isolated agents are commonly sold in a kit comprising a vial containing one agent, e. g. a protein, and a syringe or a cylinder ampoule containing the liquid agent, e. g. the solvent for said protein. When the composition is going to be used, a needle mounted on the syringe or the cylinder ampoule is passed with its pointed end through the closing rubber membrane of the vial, and the piston of the syringe or ampoule is pressed forward to press the solvent through the needle into the vial to dissolve the agent in this vial. When the agent is dissolved and a liquid composition is provided, the piston is drawn back to suck up the solution into the syringe or the ampoule. The syringe may now be used for the injection or the ampoule may be mounted in a syringe allowing the liquid composition in the ampoule to be divided into several set doses, which may be injected at time intervals.
Even during the mixing the composition may show high sensitivity and the mixing should take place without shaking the device and even adding of the solvent as a jet should be avoided. To obtain a gentle mixing the kit may comprise a plastic adaptor which may be mounted on the vial and which has means to guide the needle to an oblique position so that the solvent hits the side wall of the vial rather than the freeze dried protein itself.
Being dependant on the users skill and temper the mixing process is not a well defined process. If the users tactile motor function is reduced it may be a time consuming process to mount the adaptor on the vial, pierce the membrane of this vial, inject the solvent in the vial, wait for the freeze dried product to be solved, and sucking the solution back into the syringe, indeed it may be time consuming even for a skilled person with a good tactile motor function. Further it depends on the users temper how quickly the solvent is injected in the vial. It is recommended to perform this injection sufficiently slowly so that the solvent leaves the needle tip as drops rather than as a jet, as a jet may have a whipping effect on the composition already formed and will increase the formation of foam which is undesirable due to the fact that the foam has a high content of the solved agent which is then made unavailable. The formation of foam further causes a higher risk for air bubbles in the solution sucked back into the syringe or the cylinder ampoule and such air bubbles may have a deteriorating effect on the composition.
Another disadvantage by this known mixing kit is that the piston has to be moved first forward to inject the solvent in the vial and then backward to suck the mixture back into the ampoule. By the forward movement of the piston a part of the inner wall of the cylinder ampoule is exposed to the ambient atmosphere and contaminating material may stick to this wall which is later on brought into contact with the mixture which is sucked into the ampoule by pulling the piston backward.